Colloidal nanoparticles, especially those with active electronic and luminescent properties, have attracted a great deal of interest as components in various devices, as well as in biotechnology for use as fluorescent tags. Semiconducting nanoparticles, or quantum dots (QD's), possess significant advantages over conventional organic fluorophores in that their luminescence emission profiles are very narrow (c.a. 20-30 nm fwhm), they show good resistance to photobleaching, and absorb continuously above the bandgap. These unique properties allow for the use of multiple tags of various emissions to be excited simultaneously by a single convenient energy source of appropriate wavelength for extended periods of time.
Solubilization of nanoparticles in a given solvent system is a prerequisite to many biological and environmental applications. For example, several strategies that afford water soluble cadmium selenide (CdSe) nanoparticles for biological applications have been described recently [3, 5]. (a) Gerion, D.; Pinaud, F.; Williams, S. C.; Parak, W. J.; Zanchet, D.; Weiss, S.; Alivisatos, A. P. J. Phys. Chem. B. 2001, 105, 8861; (b) Han, M.; Gao, X.; Su. J. Z.; Nie, S. Nature Biotechnology 2001, 19, 631; (c) Mattoussi, H.; Mauro, J. M.; Goldman, E. R.; Anderson, G. P.; Sundar, V. C.; Mikulec, F. V.; Bawendi, M. G. J. Am. Chem. Soc. 2000, 122, 12142-12150. (a) Pathak, S.; Choi, S.; Arnheim, N.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4103; (b) Bruchez, M.; Maronne, M.; Gin, P.; Weiss, S.; Alivisatos, A. P.; Science 1998, 281, 2013; (c) Rosenthal, S. J.; Tomlinson, I.; Adkins, E. M.; Schroeter, S.; Adams, S.; Swafford, L.; McBride, J.; Wang, Y.; DeFelice, L. J.; Blakely, R. D. J. Am. Chem. Soc. 2002, 124, 4586; (d) Qi, L.; Colfen, H.; Antonietti, M. Nano Lett. 2001, 1, 61. It was demonstrated that CdSe/ZnS core-shell nanoparticles can be made water-soluble by subsequent introduction of a silica encapsulating shell containing ionizable end-groups. This approach, while synthetically tedious, produces photostable water-soluble CdSe nanoparticles where end-group ionization, of phosphonates for example, plays a key role. Other techniques of the prior art have relied on organic encapsulants, usually hydrophilic thiols, to solubilize the CdSe nanoparticles in aqueous media. These techniques are generally more facile, but give nanoparticles with lower stability, and pH dependent water solubility. Aldana, J.; Wang, A.; Peng, X. J. Am. Chem. Soc. 2001, 123, 8844. In particular, unwanted disulfide formation ultimately leads to nanoparticle instability.
From the preceding, it is seen that new, simple methods for preparing soluble nanoparticles yielding well-dispersed materials that retain the photoluminescent and quantum yield properties of the nanoparticles are needed in this nanotechnology field. The development of such methods and systems, together with the resulting nanoparticulate composites, remain an on-going concern in the art.